Conventionally deep freezers used for laboratories or the like are provided with a refrigerating cycle including a refrigerant circuit where a compressor, a condenser (radiator), a pressure reducing unit, an evaporator and the like are connected sequentially in a loop. This refrigerating cycle is filled with a refrigerant as well as a predetermined amount of oil to lubricate a sliding portion of the compressor. A part of this oil is discharged to the refrigerating cycle from the compressor together with the refrigerant.
The oil discharged to the refrigerant cycle hinders circulation of the refrigerant at the pressure reducing unit and the evaporator, and causes problems such as burning due to depletion of the oil in the compressor. To cope with the problem, an oil separator conventionally is provided between the compressor and the condenser.
This oil separator includes a tank with a predetermined capacity, into which a refrigerant (including oil) discharged from the compressor flows. Then, the oil in the refrigerant is separated in the tank with means such as a filter or a centrifugal separator, and the refrigerant only is made to flow out from the tank to the condenser. The oil is stored in the tank. A float provided in the tank floats at the oil level and is vertically movably held in the tank.
Accordingly, this float moves up and down with the oil level in the tank. Then, when the amount of the oil in the tank increases until the float rises up to a predetermined position with the oil level, a valve unit opens to let the oil in the tank return to the intake side of the compressor. Thereby, the oil discharged to the refrigerating cycle is returned, thus coping with the aforementioned problem (see Japanese Patent Application Laid-Open No. H9-72635 (Patent Document), for example).
Meanwhile, the refrigerant discharged from the compressor is at an extremely high pressure such as 3 MPa during the operation of the compressor. On the other hand, when the compressor stops, the pressure decreases to about 0.5 MPa. Accordingly the pressure in the oil separator also frequently changes between such a high pressure and a low pressure. Therefore the float is required to have strength to withstand such a large pressure change. The float is typically configured by welding two separated hemispheres (having a hollow inside) made of metal such as iron or stainless steel at their flanges, and the welding of high quality is required as well, thus increasing the manufacturing cost.
Additionally, due to metal fatigue inevitably generated in the float because of the pressure change with time, the float may lose the buoyancy by oil entering into the float through a broken portion. In that case, the float cannot detect up/down movement of the oil level and so the oil-returning function is unfortunately disabled.
In order to cope with such conventional technical problems, it is an object of the present invention to provide an oil separator capable of preventing the breakage of a float with an extremely simple configuration and a refrigerating cycle apparatus using the same.